Bleach activators are important constituents in detergents, stain removal salts and dishwashing detergents. They permit a bleaching action even at temperatures below 60.degree. C. by reacting with a source of hydrogen peroxide--in most cases perborates or percarbonates--to release an organic peroxy acid.
Suitable bleach activators are many reactive organic compounds having an O-acyl or N-acyl group. Representative examples such as N,N,N',N'-tetraacetylethylenediamine (TAED), glucose pentaacetate (GPA), xylose tetraacetate (TAX), sodium-4-benzoyloxybenzenesulfonate (SBOBS), sodium trimethylhexanoyloxybenzenesulfonate (STHOBS), tetraacetylglucoluril (TAGU), tetraacetylcyanic acid (TACA), di-N-acetyldimethylglyoxine (ADMG) and 1-phenyl-3-acetylhydantoin (PAH) are described in Patents GB-A-836 988, GB-A-907 356, EP-A-0 098 129 and EP-A-0 120 591.
In the meantime, cationic bleach activators which contain a quaternary ammonium group have gained in importance since they are highly effective bleach activators. Such cationic bleach activators are described, for example, in GB-A-1 382 594, U.S. Pat. No. 4 751 015, EP-A-0 284 292 and EP-A-0 331 229.
Ammonium nitrites of the formula EQU R.sup.1, R.sup.2.spsp..sym., R.sup.3 NCH.sub.2 CN X.sup..crclbar.
in which R.sup.1, R.sup.2 and R.sup.3 are alkyl, alkenyl or aryl groups, are a particular class of cationic bleach activators. Compounds of this type and their use as bleach activators in bleaches are described in EP-A-303 520, EP-A-464 880, EP-A-458 396 and U.S. Pat. No. 4,883,917. In all of the compounds described therein, the nitrogen atom of the ammonium group is substituted by alkyl, alkenyl or aryl groups. Another class of ammonium nitrites is described in German Patent Application 19 605 526.
Normally, bleach activators are used in granulated form in detergents in order to ensure an adequate storage stability and in order to release the bleaching effect only in the wash.
For granulating bleach activators, numerous auxiliaries and processes have been described in the past. EP-A-0 037 026 describes a process for preparing readily soluble activator granules comprising between 90 and 98% by weight of activator. For this purpose, the pulverulent bleach activator is homogeneously mixed with likewise pulverulent cellulose ethers or starch ethers and then sprayed with water or an aqueous solution of the cellulose ether, simultaneously granulated and then dried.
According to EP-A-0 070 474, it is possible to prepare similar granules by spray drying aqueous suspensions comprising the activator and the cellulose ether. Granules consisting of bleach activator, cellulose ethers and additives of an organic C.sub.3 -C.sub.6 -carboxylic or hydroxycarboxylic acid are described in WO 90/01535 and WO 92/13798. While in WO 90/01535, the organic carboxylic acid is incorporated into the granule core in order to accelerate its solubility, in WO 92/13798, the carboxylic acid is deposited on the finished granule in an additional coating stage. The protective acid coating should prevent spotting of the bleach and contribute to preserving the color of the fabric. WO 94/03395 claims the use of acidic polymer compounds having a solubility in water of &gt;5 g/l (at 20.degree. C.) and molecular weights of from 1000 to 250,000 for the same purpose. Granules of bleach activators in which mixtures of soaps and free fatty acids are used as granulating auxiliaries are likewise known (GB-A-1 507 312).
A water-free preparation process is known from EP-A-0 075 818. Here, the bleach activator, together with an organic binder, for example a fatty alcohol ethoxylate, is compressed by compaction under pressure to give particles having diameters of from 0.5 to 3 mm.
For most of the specified granulation processes, it is a prerequisite that the bleach activator to be granulated is a solid and has a high melting point. This is necessary in order that during preparation it does not react with the binder or water present and decompose. Thus, in DE-A 2 048 331, for example, preference is given to activators which have a melting point of preferably at least 100.degree. C., in particular at least 150.degree. C.
The binders which have hitherto been used are predominantly organic compounds. This can, however, cause problems which limit the use of the granules.
If surface-active compounds are used, such as soaps, fatty acids, anionic surfactants or fatty alcohol ethoxylates, then the granules prepared therewith are unsuitable for use in dishwashing detergents since problems with foam arise under the washing conditions. This is even the case when normally low-foam highly ethoxylated fatty alcohols are used. For use in dishwashing detergents therefore, activator granules whose binder consists of cellulose ethers are predominantly used. The biodegradability of this group of products is, however, moderate.
A further problem relates to suitable granules for use in stain removal salts. Modern formulations consist of mixtures of percarbonate and bleach activator granules. In order to prevent exothermic decomposition of these mixtures during preparation and storage, inert materials, such as sodium carbonate, sodium hydrogencarbonate or sodium sulfate, are frequently added. For this field of application, inert binders or coating agents would be of great interest.
Inorganic materials as carriers for bleach activators are known per se. For example, DE-A 2 733 849 proposes the adsorption of liquid activators, such as diacetylmethylamine, diacetylbutylamine or acetyl caprolactam on inorganic adsorbents, such as kieselguhr, magnesium aluminum silicates, sodium or calcium aluminum silicates, activated silica or aluminum oxide.
Furthermore, according to GB-A 2 249 104, it is possible to prepare particles in which a bleach activator solid per se is deposited in finely divided form on an inorganic carrier material. For this purpose, activator and carrier material are firstly intimately mixed, and an organic solvent (ethanol or toluene) is added, as a result of which the activator goes into solution. By subsequently distilling off the solvent, the activator is deposited in very finely divided form on the carrier. The preferred particle size distribution of the particles according to the invention is between 60 and 250 .mu.m.
In addition, EP-A-0 240 057 discloses bleach activator granules which are prepared by mixing an activator with inorganic or organic salts, film-forming polymers and small amounts of smectites or aluminum silicates and subsequently granulating the mixture in the presence of water. Once granulation is complete, a costly drying stage is necessary in order to obtain storage-stable granules.
Bleach activator granules which are obtained by mixing and compressing dry bleach activator and smectites (bentonite) in the absence of water are known from DE-A 44 39 039. The bleach activator used therein is essentially only TAED. The influence of TAED on the washing performance is, however, essentially independent of whether the TAED is in granulated form or in powder form.